DaoistuDBhcT
The Light Magic Talent being "Genius" but "C" tier is confusing, but it seems like the MC is confused too. Since Light Magic is fairly specific it makes sense that it's C tier. But a "C" tier in MC's classification being also a Genius rank talent seems to be unexpected and goes against the norm, which to me seems like a purposeful move by the author, rather than something that breaks our understanding of Talent rankings (thank god)
Regarding the confusion on the C rank talent. if I recall right, it was stated in the beginning that the longer the name of a talent the worse it is. So if his talent was just simply "Magic" it would be S tier."magic power-light element" is c tier.So something like "Magic Power" would be A tier. At least that's how I understand it.